The invention relates to a switch acting in contactless fashion.
DE 103 37 660 A1 has disclosed a switch acting in contactless fashion for a rolling door controller, which produces switching signals corresponding to the position of a movable rolling door at a controller for the purpose of adapting the moving speed of the rolling door depending on the respective position, in order that the rolling door is accelerated optimally, moved quickly and moved slowly into the respective end position. For this purpose, passive RFID transponders are arranged along the side edge of the rolling door and act as actuators for a sensor, which is fixed in position on a rolling door frame, of the switch. In this case, the sensor transmits an interrogation signal via a coil of a transceiver supplied with power and recognizes a position of the rolling door as soon as an RFID transponder sends a response signal back as a result of a sufficient proximity to the coil. The accuracy of the determination of the position which can be achieved with the known switch is thus dependent on the shape of the radiation lobe of the electromagnetic field emitted by the transceiver and is thus low in practice. The known switch is therefore not suitable for accurate determination of the position of the moving part in order, for example, to establish whether a protective door is sufficiently closed in order to be held closed securely by a tumbler acting in contactless fashion.
In order to precisely monitor the position of a moving part with respect to a fixed part, inductive proximity switches are known which provide a voltage signal dependent on the distance between the two parts, cf. DE 44 27 283 C1, for example. However, these apparatuses are independent and require a dedicated sensor and a dedicated evaluation circuit.